About JNI.***.dll already loaded in another class loader.

About JNI.***.dll already loaded in another class loader.
When I run a WEB program that use's JNI and DLL.The following excetpion information is throwed:
.***.dll already loaded in another class loader.(string "***" represents a dll name).
Help! Who can provide a solution.
Thanks.

i got the same problem before. seems it happens when
you load the .dll not using static{ } block. And when
your web application got an error and you fix it to
restart your application without restarting your
server, you will get this error message. You can
either put load library stuff in the static{ } block
or restart your server.And again.......
If all you want is to have the dll loaded, and it is loaded (that is why the exception occurs) then it does not matter that the exception occurs. You can catch it and ignore it.

Similar Messages

System class loader vs application class loader

Hello
I have a class that uses a third partyjar which I have put in /jre/lit/ext. The class compiles but fails at runtime being unable to read the property files called in the class' constructor. I believe that is b/c the third party jars are loading w/ the system class loader and cannot "see" the property files "floating" at the same level as the class that is calling them.
So I created a jar, of the property files, with the same directory/package structure as the location of the property files and put that in the /jre/lib/ext and STILL the same problem; cannot read the property files, the constructor fails, fugly. There is an overloaded constructor that includes a parameter for the property files, but I need to get this to work as is first. What am I missing? Please edify me. tia.

If the 3rd party jar needs a certain properties file to initialize correctly, I doubt it would be looking for it in the class hierarchy. I mean I doubt it does:
Properties p = new Properties();
p.load( getClass().getResourceAsStream() );It's more likely to do:
Properties p = new Properties();
p.load( new FileInputStream(...) );The reason is that the property file should be easily edited by the user and users know how to move around in the file system, not in the Java jars and classpaths.
Just a guess...

Can I set Boot class loader or system class loader?

In my application, there are classes in a jar files, all these files in the jar need be loaded by a ClassLoader in my application.
And the classes out of jar do not need the ClassLoader to load. the structure is like :
-----myapp.jar ------in this jar, all classes need be loaded by a specified ClassLoader
|---anoapp ------classes in this package, is normal classes
|-------|----a.class
|----b.class
| ----other classes
but my a.class need to access a class in myapp.jar, so I load the class use my ClassLoader, but there still occur
**********ClassFormatError : bad magic number**************
I print the classloader in a.class
+---- System ClassLoader is : com.sun.misc.Launcher$AppClassLoader    ------------it is not my ClassLoader
+---- a.class.getClassLoader is same as System ClassLoader    -------------------it still is not my ClassLoader
+---- Thread.currentThread().getContextClassLoader          ------------------ it is my ClassLoader
So I think when I access class in myapp.jar, it will loaded by System ClassLoader or Bootstrap ClassLoader, if I can set one these two classloader as my ClassLoader, it maybe not occur the Error,
But There are not obvious method in System or Runtime etc.
1. So can Set System Classloader or Bootstrap ClassLoader?
2. If not, How can solve my problem?
Thands in advanced!

**********ClassFormatError : bad magic number**************If you get that error, then no classloader will help you. This is a problem with your running code meant for a newer version of the Virtual Machine in an older version.
Looks like you're compiling the code with a recent JDK (1.4.x?), but running with an older VM. Try just typing "java -version" and see what it prints.
This should just be a matter of running with the right VM. If this is an applet you're trying to run inside the browser, make sure that the browser is using the right VM. Run the "Java Control Panel" and select the correct version.

Class loader probelm

Hi all,
I am using IAS 6.0 with sp1 on windows NT system .I deployed my applications in two servers which are in a cluster.I deployed two applications using one dll file.When I am navigating through the site , first i gone through one application accessing that dll , i am not getting any error.After that I accessed second application accessing the same dll I got one error that:
Java.lang.unsatisfiedlinkerror :execution failed and dll is already loaded by another class loader.
Please mail me immediately .
Thanks & regards,
Usha

hi usha,
Check out the Article ID: 2361 at iplanet knowledgebase
that will helps you.
regards,
saravanan

Dynamic Class Loading in an EJB Container

Hello,
We have a need to load classes from a nonstandard place with in an ejb container, ie a database or secure store. In order to do so we have created a custom class loader. Two issues have come up we have not been able to solve, and perhaps some one knows the answer to.
Issue 1.
Given the following code:
public static void main(String args[])
MyClassLoader loader = new MyClassLoader("lic.dat");
System.out.println("Loading class ..." + "TestObject");
Object o = Class.forName("TestObject",true,loader).newInstance();
System.out.println("Object:" + o.toString());
TestObject tstObj = (TestObject) o;
tstObj.doIt();
What happens when executed is as follows. Class.forName calls our loader and does load the class as we hoped, it returns it as well, and the o.toString() properly executes just fine. The cast of the object to the actual TestObject fails with a class not found exception. We know why this happens but don't know what to do about it. It happens because the class that contains main was loaded by the system class loader (the primordial class loader as its sometimes called), That class loader does not know about TestObject, so when we cast even though the class is "loaded" in memory the class we are in has no knowledge of it, and uses its class loader to attempt to find it, which fails.
> So the question is how do you let the main class know to use our class loader instead of
the system class loader dispite the fact is was loaded by the system class loader.
Issue 2:
To make matters worse we want to do this with in an EJB container. So it now begs the question how do you inform an EJB container to use a specific class loader for some classes?
Mike...

Holy crap! We are in a similar situation. In creating a plugin engine that dynamically loads classes we use a new class loader for each plugin. The purpose is so that we can easily unload and/or reload a class at runtime. This is a feature supposedly done by J2EE app servers for hot-deploy.
So our plugins are packaged as JAR files. If you put any class in the CLASSPATH, the JVM class loader (or the class loader of the class that is loading the plugin(s)), will load the class. The JavaDoc API states that the parent classloader is first used to see if it can find the class. Even if you create a new URLClassLoader with NULL for parent, it will always use the JVM class loader as its parent. So, ideally, in our couse, plugins will be at web sites, network drives, or outside of the classpath of the application and JVM.
This feature has two benefits. First, at runtime, new updates of plugins can be loaded without having to restart the app. We are even handling versions and dependencies. Second, during development, especially of large apps that have a long startup time, being able to reload only one plugin as opposed to the annoying startup time of Java apps is great! Speeds up development greatly.
So, our problem sounds just like yours. Apparently, the Client, which creates an instance of the plugin engine, tries to access a plugin (after the engine loades it via a new classloader instance for each plugin). Apparently, it says NoDefClassFound, because as you say, the client classloader has no idea about the plugin class loaded by another classloader.
My co-developer came up with one solution, which I really dont like, but seems to be the only way. The client MUST have the class (java .class file) in its classpath in order to work with the class loaded by another class loader. Much like how in an EJB container, the web server calling to EJB MUST contain the Home and Remote interface .class files in its classpath, the same thing needs to be done here. For us, this means if a plugin depends on 5 others, it must contain ALL of the .class files of those plugins it depends on, so that the classloader instance that loads the plugin, can also see those classes and work with them.
Have you got any other ideas? I really dislike that this has to be done in this manner. It seems to me that the JVM should be able to allow various class loaders to work with one another in such a way that if a client loaded by one classloader has an import statement in it to use a class, the JVM should be able to fetch the .class out of the other classloader and share it, or something!
This seems to me that there really is no way to actually properly unload and then reload a class so that the JVM will discard and free up the previous class completely, while using the new class.
I would be interested in discussing this topic further. Maybe some others will join in and help out on this topic. I am surprised there isn't a top-level forum topic about things like class loaders, JVM, etc. I wish there was a way to add one!

Dynamic class loading from JARs in web application

Hello,
I'm working on a web project in which we would like to dynamically load plugins without server restart.
We have developed our own ClassLoader in order to load the plugins from a path or with a user interface upload function.
The class loader hierarchy should be something like this:
      Bootstrap
          |
       System
          |
       Common
Catalina   Shared
        Webapp1 OurSystem
                   PluginClassLoaderThe all works fine within the classes loaded in the PluginClassLoader, but classes loaded in OurSystems class loader cannot access classes loaded in PluginClassLoader. For example when Hibernate tries to load classes definied in mapping files we got a java.lang.ClassNotFoundException.
Is there a way to load classes dynamically to OurSystems class loader or notify it about PluginClassLoaders classes?
Or is this a bad way to do it?
Best regards,
Kristoffer Renholm

Hi,
Sounds like a classpath problem that the folks in the workshop newsgroup
could help with. Try asking your question in:
http://newsgroups.bea.com/cgi-bin/dnewsweb?cmd=xover&group=weblogic.developer.interest.workshop&utag=
Bruce
Graeme Dougal wrote:
>
Hi, I am developing a web service with weblogic workshop. The JWS file references
other classes one of which is a factory for distributing various implementations
of an interface. I am trying to dynamically load the relevant class to be distributed
from the factory via its name, e.g. Class c = Class.forName(className)
However I keep getting a classNotFoundException.
Any ideas ??

Dynamic class loading when CODEBASE is unreachable. A bug?

Let us suppose that we have a large-scale distributed application with ca. 1000 participants communicating via RMI and utilizing dynamic class loading. As we all know, a HTTP code server must be available for this purpose in order to provide dynamically downloaded code, usually the communication proxy code of remote objects. In a real-world scenario, the HTTP server will never be 100% available, so that we will have cases that a Java process will not be able to download the necessary Java classes, causing the RMI communication to fail with a ClassNotFoundException or similar exception. In such a case, a robust application would perform some recovery activities and retry the remote call. Eventually, the HTTP server becomes available again and the distributed system recovers automatically. This seems to work fine with J2SE 1.4.2_10, but not with 1.4.2_11 and newer versions. Considering Java 5, the Update 9 exhibits the same problem.
For tracking down the problem, I've written a simple distributed test application, consisting of a client and a server. A server listens on a port, and sends a MarshalledObject to the client. The code of the MarshalledObject is annotated with the value of the "java.rmi.server.codebase" system property. The annotation contains an URL of the JAR file containing the code of the original object. The client connects to the server, reads data form the socket and unmarshalls the original object. This is basically the same procedure as when objects are accross the wire as arguments/return values/exceptions by the RMI/JRMP engine. This procedure is repeated forever in the loop. Due to the fact that the client's CLASSPATH doesn't contain the code of the original object, this code should dynamically be loaded from the HTTP server using the appropriate annotation provided by the server.
If we start the client while the HTTP server is down, the client will keep generating the ClassNotFoundException over and over again, as expected. So far, so good. If we now start the HTTP server while the client is still running, we will observe different behaviors, depending on the version of the client's JVM:
1. In J2SE 1.4.2_10, the client will download the code from the HTTP server and successfully unmarshal the original object sent by the server. ClassNotFoundExceptions will not be generated again.
2. In J2SE 1.4.2_11, 1.4.2_12 and 1.4.2_13 as well as in J2SE 5.0 Update 9, the client will continue generating ClassNotFoundExceptions. Analysis of the HTTP server's access log shows that there were no attempts to download the JAR file required for unmarshaling the object sent by the server.
It seems that in the newer JVM versions the RMI engine remembers URLs which have failed and does not attempt to access them anymore. Althogh this may have some advantages considering the overall network load, the dynamical class loading becomes practically useless in productive large distributed systems. The very first attempt to load the codebase of the communication peer must succeed, otherwise the whole process must be restarted for the communication to work, which is a very expensive (and for most customers unacceptable) operation in terms of preformance and resources usage.
Should this be seen as a bug or a feature of the JVM? What do you think?
Regards,
Miran
Here is the code to reproduce:
Server code
package server;
import java.net.*;
import java.rmi.*;
import java.io.*;
public class Server implements Serializable {
private int value = 42;
public Server() {
public String toString() {
    return "The Answer is " + value;
public static void main( String[] args ) {
    if( args.length!=1 ) {
      System.out.println( "Usage: server.Server <port>" );
      System.exit( 1 );
    try {
      MarshalledObject data = new MarshalledObject( new Server() );
      int port = Integer.parseInt( args[0] );
      ServerSocket serverSocket = new ServerSocket( port );
      System.out.println( "Accepting connections..." );
      while( true ) {
        Socket s = serverSocket.accept();
        new Thread( new SocketHandler( s, data ) ).start();
    } catch( Exception ex ) {
      ex.printStackTrace();
    System.exit( 0 );
public static class SocketHandler implements Runnable {
    private Socket s;
    private Serializable data;
    public SocketHandler( Socket s, Serializable data ) {
      this.s = s;
      this.data = data;
    public void run() {
      try {
        OutputStream os = s.getOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream( os );
        oos.writeObject( data );
        oos.close();
        os.close();
        s.close();
        System.out.println( "Serving socket succeeded" );
      } catch( Exception ex ) {
        System.out.println( "Serving socket failed" );
        ex.printStackTrace();
Client code
package client;
import java.rmi.*;
import java.net.*;
import java.io.*;
public class Client {
public static void main( String[] args ) {
    if( args.length!=1 ) {
      System.out.println( "Usage: client.Client <port>" );
      System.exit( 1 );
    try {
      if( System.getSecurityManager()==null ) {
        System.setSecurityManager( new RMISecurityManager() );
      int port = Integer.parseInt( args[0] );
      for( int i = 1; true; ++i ) {
        try {
          Socket s = new Socket( "localhost", port );
          InputStream is = s.getInputStream();
          ObjectInputStream ois = new ObjectInputStream( is );
          Object o = ois.readObject();
          ois.close();
          is.close();
          s.close();
          Object umo = ((MarshalledObject) o).get();
          System.out.println( i + ". Retreiving MarshalledObject succeeded: "
                              + umo );
        } catch( Exception ex ) {
          System.out.println( i + ". Retreiving MarshalledObject failed" );
          ex.printStackTrace();
        System.out.println( i + ". Waiting for 10 sec" );
        Thread.sleep( 10000 );
    } catch( Exception ex ) {
      ex.printStackTrace();
    System.exit( 0 );
Start command for the server
java -cp server.jar -Djava.rmi.server.codebase="http://localhost/playground/server.jar" server.Server 33933
Start command for the client
java -cp client.jar -Djava.security.policy=all.policy client.Client 33933
The policy.all file should look as follows
// All permissions
grant {
   permission java.security.AllPermission;
};The server.jar file should only contain the classes from the server package. This file should also be made accessible via HTTP (e.g. by using the Apache HTTP server).
The client.jar file should only contain the classes from the client package.

no body know about this??

Transient / network class loader

i hope to understand exactly what "transient" means in the context of remote class loading.
i am serializing an object on a local machine.
send it over a socket to remote machine.
remote machine de-serializes.
it needs the classes to de-serialize.
calls back to the local machine.
gets the classes.
ok.
issue:
i am looking at the classes that the { java.io.ObjectInputStream "resolveClass(ObjectStreamClass desc);" }
is requesting for loading during the de-serialization process.
and see that the classes for the objects that i marked as "transient" are still being requested.
i did not expect this.
my marking objects as "transient" means those objects are not a part of an object's persistent "state".
yet, the classes for the transient objects are still requested.
do i not understand transient?

i hope to understand exactly what "transient" means in the context of remote class loading.The context is irrelevant. 'transient' has the same meaning in all contexts. It means the field(s) so marked is/are ignored by Java Serialization.
and see that the classes for the objects that i marked as "transient" are still being requested.By the class loader. The class loader doesn't care about 'transient'. The receiver will still need those classes if it uses that field. The class loader can't assume that it won't do that. So it loads the classes of the transient objects. Just like it loads the superclasses, and the classes of all the other fields, member and static.

Codebase classes loading on their own?

I have been tracking down a performance issue. So I am tracing the classes loaded by my clients VM. I have a class defined like so
public final class GraphicFactory implements IGraphicFactory, Serializable{
     private static final long serialVersionUID = 1L;
     public IDSComponentInstance createComponentInstance(Point location, Dimension size){
        if (location == null || size == null) {
            throw new NullPointerException();
        return new DBComponentInstance(location,size);
    public IDSFunctionConnection createFunctionConnection(Point sourceLocation, Point targetLocation) {
        if(sourceLocation == null || targetLocation == null){
            throw new NullPointerException();
        return new DBFunctionConnection(sourceLocation,targetLocation);
}I want to pass this class to the client. So the client calls a method, and this class is returned. When that happens, the client immediately loads this class via the codebase. The thing I can not see is when the client loads the "DBFunctionConnection" and "DBComponentInstance" classes. These classes are also in jar files which can be found by the codebase. Obviously the client is getting them because its working. And they are definitely coming from the server. But I do not see any log of them being loaded.
Its like they get loaded in secret. I bet they do too. I think classes loaded as a result of another class loading are not logged.
But at the same time, I thought a class would not be loaded until it is needed!? If its loading it right away, then this is a good thing because otherwise the RMI system could throw an exception at a most unusual place when the class gets loaded because a method is called.
I can't quite figure out what is happening here :(

I guess RMI classloader is just different.
From testing I can see that when the main class is
marshalled it seems as if the classes it contains are
also marshalled.RMIClassLoader is little more than a URLClassLoader. Classes are neither marshalled nor unmarshalled in RMI, they are loaded via the codebase mechanism, using whatever WEB or other protocol you define in the codebase URL.
The log is not telling me when classes are loaded,So you're logging the wrong thing?
So I am still stuck having a hard time knowing when
the RMI is transferring classes.RMI isn't transferring classes. The RMIClassLoader is transferring classes in response to class-loading requirements. This is completely separate from RMI marshalling. It is more strongly associated with RMI unmarshalling but these are still distinct operations.

Class Loader Differences

Hi!
I found differences in beheviour of system class loader and OJSP class loader.
The problem is:
when I place jar's in web-inf\lib directory I get message about impossibility to find classes (not all, just some).
When I use servlet engine wrapper.classpath parameter evething works fine.
Any comments will be appreshiated
Mike

You may have encountered bug 1625520 -
JSPC DOES NOT USE INCLUDE CLASSES UNDER
WEB-INF DIRECTORIES .
The bug was recently fixed (version 1.1.2.1
which should be going out with the 9i database or that or a higher version of the
OJSP should be going out on OTN shortly.
By shortly, I'm guessing beginning of
April.

How to improve class-loading performance for missing classes

Hi,
do you have any ideas how we can improve the class-loading performance on a weblogic 12c running on jrockit? We spend about 20-30 ms per request in class-loading due to the way hibernate criteria API works (it tries to load quite a lot of missing classes). The only thing I came up with was to invert the class-loading using the weblogic descriptor for those missing classes (which are actually no real classes but some parts of a generated JPQL) which does improve performance a bit.
Thanks
Dimo

Hi,
do you have any ideas how we can improve the class-loading performance on a weblogic 12c running on jrockit? We spend about 20-30 ms per request in class-loading due to the way hibernate criteria API works (it tries to load quite a lot of missing classes). The only thing I came up with was to invert the class-loading using the weblogic descriptor for those missing classes (which are actually no real classes but some parts of a generated JPQL) which does improve performance a bit.
Thanks
Dimo

Application Class Loader problem calling virtual function

Hello everyone
I have run in to very strange behavior of JVM
I have created a class loader which allows my to load classes from
jar file, regardless that URLClassLoader supplies this functionality.
I am using this class loader to load some classes and call their virtual functions. The class diagram looks like that:
public interface I {
   public void init();
public class AAA implements
   public void init(){
public class BBB extends AAA{
   public void init(){
      //here comes implementation
}Interface I and class AAA are loaded with System Class loader and Class BBB is loaded using my class loader from jar file.
ByteStreamClassLoader classLoader = new ByteStreamClassLoader ();
Class cl = classLoader. loadClass(�com.product.BBB�,true);
I myInterface = cl.newInstance();
myInterface.init();The problem is that from some unknown reason java class AAA.init() instead of BBB.init().
Can somebody help me what am I doing wrong?
Class Loader code attached below
public class ByteStreamClassLoader   extends ClassLoader {
    protected HashMap m_cache = new HashMap();
    public void clearCashe() {
      m_cache = new HashMap();
    private String definePackage(String className) {
      StringBuilder strB = new StringBuilder();
      //Class name must be removed from the URI in order to define a package
      String[] packageArray = className.split("\\.");
      for (int i = 0; i < packageArray.length - 1; i++) {
        strB.append(packageArray).append(".");
String packageName = strB.toString();
packageName = packageName.substring(0, packageName.length() - 1);
if (getPackage(packageName) == null) {
m_logger.log(Level.FINEST, "Defining package '" + packageName + "'");
definePackage(packageName, null, null, null, null, null, null, null);
return packageName;
public synchronized Class loadClass(String name, boolean resolve) throws
ClassNotFoundException {
name = name.replaceAll("/", ".").replaceAll(".class", "");
//Try to locate the Class in cashe
Class c = (Class) m_cache.get(name);
//Try to locate the Class in the System Class Loader
if (c == null) {
try {
c = ClassLoader.getSystemClassLoader().loadClass(name);
catch (Exception ex) {}
else {
m_logger.log(Level.FINEST, "Class '" + name + "' found in cache");
//Load the class from byte array
if (c == null) {
String resourceName = name;
if (!resourceName.endsWith(".class")) {
resourceName = resourceName.concat(".class");
//Retrieve class byte representation
if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

Hello everyone
I have run in to very strange behavior of JVM
I have created a class loader which allows my to load classes from
jar file, regardless that URLClassLoader supplies this functionality.
I am using this class loader to load some classes and call their virtual functions. The class diagram looks like that:
public interface I {
   public void init();
public class AAA implements
   public void init(){
public class BBB extends AAA{
   public void init(){
      //here comes implementation
}Interface I and class AAA are loaded with System Class loader and Class BBB is loaded using my class loader from jar file.
ByteStreamClassLoader classLoader = new ByteStreamClassLoader ();
Class cl = classLoader. loadClass(�com.product.BBB�,true);
I myInterface = cl.newInstance();
myInterface.init();The problem is that from some unknown reason java class AAA.init() instead of BBB.init().
Can somebody help me what am I doing wrong?
Class Loader code attached below
public class ByteStreamClassLoader   extends ClassLoader {
    protected HashMap m_cache = new HashMap();
    public void clearCashe() {
      m_cache = new HashMap();
    private String definePackage(String className) {
      StringBuilder strB = new StringBuilder();
      //Class name must be removed from the URI in order to define a package
      String[] packageArray = className.split("\\.");
      for (int i = 0; i < packageArray.length - 1; i++) {
        strB.append(packageArray).append(".");
String packageName = strB.toString();
packageName = packageName.substring(0, packageName.length() - 1);
if (getPackage(packageName) == null) {
m_logger.log(Level.FINEST, "Defining package '" + packageName + "'");
definePackage(packageName, null, null, null, null, null, null, null);
return packageName;
public synchronized Class loadClass(String name, boolean resolve) throws
ClassNotFoundException {
name = name.replaceAll("/", ".").replaceAll(".class", "");
//Try to locate the Class in cashe
Class c = (Class) m_cache.get(name);
//Try to locate the Class in the System Class Loader
if (c == null) {
try {
c = ClassLoader.getSystemClassLoader().loadClass(name);
catch (Exception ex) {}
else {
m_logger.log(Level.FINEST, "Class '" + name + "' found in cache");
//Load the class from byte array
if (c == null) {
String resourceName = name;
if (!resourceName.endsWith(".class")) {
resourceName = resourceName.concat(".class");
//Retrieve class byte representation
if (resourceName.indexOf(".") != -1) {
resourceName =
resourceName.replaceAll("\\.", "/").replaceAll("/class", ".class");
//Use the ByteStreamClassLoader to load the class from byte array
byte[] classByteArray = null;
try {
classByteArray = getResourceBytes(resourceName);
catch (IOException ex1) {
throw new ClassNotFoundException(
"Could not load class data." + ex1.getMessage());
m_logger.log(
Level.FINEST, "Loading class '" +
name + "' Byte Length: " + classByteArray.length);
String p = definePackage(name);
c = defineClass(
name,
classByteArray,
0,
classByteArray.length,
ByteStreamClassLoader.class.getProtectionDomain());
m_cache.put(name, c);
if (resolve) {
resolveClass(c);
return c;

Class loader question

Hi,
I got NoClassDefFoundError and when I use ClasspathDebug jsp it shows that the class is loaded by "java.net.URLClassLoader". I put the jar file containing the class in <domain>/lib directory. According to docs the jar under <domain>/lib should be loaded by system class loader. what is "java.net.URLClassLoader"? why isn't system loader loading my class? I am using wls91. Thanks
weblogic.servlet.jsp.TagFileClassLoader
weblogic.utils.classloaders.ChangeAwareClassLoader
weblogic.utils.classloaders.GenericClassLoader
weblogic.utils.classloaders.GenericClassLoader
java.net.URLClassLoader
sun.misc.Launcher$AppClassLoader
sun.misc.Launcher$ExtClassLoader
Bootstrap classloader

I'm not sure from reply 2 whether you figured out what's going on or not. It sounds like you did, but just in case...
The null/primordial/bootstrap class loader loads classes in the core API--stuff it finds in the ext dir(s?) (e.g. rt.jar)--Object, String, java.util.*, java.sql.*, etc. It has no parent. It is the root of the normal delegating classloader tree.
The system classloader is the one that uses classpath to load your classes and 3rd party classes. Everything not in the core API, as long as neither you nor those other classes explicitly specify a different classloader.
The way the normal delegation mechanism works is that a request to load a class is first passed to the loader that loaded the current class. This loader first gives its parent a chance to load it, and so on up the tree to the primordial loader.
Once it hits the root (null/primordial/bootstrap), that classloader tries to load it. If it can't (and the primordial loader can't, in fact, load your class, since it's not in the ext dir), then it hands it back to its child. This continues down the line, with the parent getting first shot at loading, then the child trying if the parent fails.
The primordial loader (which loaded the JdbcOdbcDriver) can't load your class. It hands it back to its child--the system classloader--which can and does load it, using classpath.
I hope that answers any lingering questions, if there were in fact such questions.

Class Loader for Jar Files

I have a set of Jar files which i need to load using Custom Class Loader. Any one who has Javacode for Custom Class Loader for loading Jar files send it. The Jar files are local jar files.

Here is the class loader I use:
import java.net.URL;
import java.net.URLClassLoader;
import java.net.JarURLConnection;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.InvocationTargetException;
import java.util.jar.Attributes;
import java.io.IOException;
* A class loader for loading jar files, both local and remote.
public class JarClassLoader extends URLClassLoader {
    private URL url;
    private URL[] m_urlList = new URL[10];
     * Creates a new JarClassLoader for the specified url.
     * @param url the url of the jar file
    public JarClassLoader(URL url,ClassLoader cl) {
         super(new URL[] { url },cl);
      this.url = url;
    public JarClassLoader(URL[] urlList,ClassLoader cl) {
         super( urlList,cl);
      this.m_urlList = urlList;
     * Returns the name of the jar file main class, or null if
     * no "Main-Class" manifest attributes was defined.
    public String getMainClassName() throws IOException {
      URL u = new URL("jar", "", url + "!/");
         JarURLConnection uc = (JarURLConnection)u.openConnection();
         Attributes attr = uc.getMainAttributes();
         return attr != null ? attr.getValue(Attributes.Name.MAIN_CLASS) : null;
     * Invokes the application in this jar file given the name of the
     * main class and an array of arguments. The class must define a
     * static method "main" which takes an array of String arguemtns
     * and is of return type "void".
     * @param name the name of the main class
     * @param args the arguments for the application
     * @exception ClassNotFoundException if the specified class could not
     *            be found
     * @exception NoSuchMethodException if the specified class does not
     *            contain a "main" method
     * @exception InvocationTargetException if the application raised an
     *            exception
     public void invokeClass(String name, String[] args) throws ClassNotFoundException,
            NoSuchMethodException,
            InvocationTargetException
         Class c = loadClass(name);
         Method m = c.getMethod("main", new Class[] { args.getClass() });
         m.setAccessible(true);
         int mods = m.getModifiers();
         if (m.getReturnType() != void.class || !Modifier.isStatic(mods) || !Modifier.isPublic(mods)) {
         throw new NoSuchMethodException("main");
         try {
           m.invoke(null, new Object[] { args });
         } catch (IllegalAccessException e) {
         // This should not happen, as we have disabled access checks
}

Spacename of a class loader

Question:
Does a class loader stores references for any class loaded by its parents after a request from itself to load a class? In this way the set of classes loaded for a class loader and the returned ones by its parent after a request would comprise the spacename of this class loader.

i think so. the class loader if unable to load the class actually asks its parent class loader to load the class (since its a parent delegation model) and thus acts as the initiating class loader for that type. Thus it adds the type name to the list maintained by it. Next time when the type is referenced, it first check this list (its namespace) and and if it finds it, it loads it otherwise it delegates it to its parent.
G.P.

About JNI.***.dll already loaded in another class loader.

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